1. Field of the Invention
This invention relates to a method of removing water from butylene oxides. More particularly, this invention relates to drying 1,2-butylene oxide; cis- or trans-2,3-butylene oxide isobutylene oxide; or mixtures thereof. This invention also relates to a process for removing impurities from butylene oxides by subjecting a crude butylene oxide stream, which cannot be easily purified by conventional distillation processes, to extractive distillation with suitable solvents. This invention still further relates to the resolution of crude 1,2-butylene oxide-containing mixtures produced by the epoxidation of 1-butylene by an organic hydroperoxide.
2. Description of the Prior Art
Alkylene oxides may be prepared from olefins by direct oxidation with oxygen; by oxidation with an oxidizing agent such as hydrogen peroxide, peracetic acid, or an organic hydroperoxide; or by conversion of halohydrins (prepared from the olefins) by the action of the base. Alkylene oxides are useful as polymerizable monomers, but they must be in a highly pure form for this purpose.
Alkylenes oxides obtained by direct oxidation or by oxidation with an oxidizing agent contain impurities including water and oxygen-containing organic compounds such as aldehydes, ketones, esters, alcohols, inorganic esters. Suggested methods for removing impurities include distillation (as well as extractive distillation) and chemical treatments. An example of the latter method is hydrolysis of esters and neutralization of acids with an alkali solution followed by distillation. Chemical treatments are generally undesirable because of associated product losses.
Purification of butylene oxides by means of distillation alone is difficult because of close-boiling impurities and formation of azetropic mixtures. Unlike ethylene or propylene oxides, butylene oxides form azetropes with water at atmospheric pressure. These azetropes are not readily separable by fractional distillation. Therefore, purification methods used in ethylene oxide and propylene oxide processes are not necessarily applicable to the purification of butylene oxide.
U.S. Pat. No. 2,779,721 suggests drying wet butylene oxides by liquid extraction of butylene oxide with a strong aqueous solution of an alkali metal hydroxide at a temperature below about 50.degree. C. Up to 87% of the water can be removed from the mixture of butylene oxides containing 80% 1,2-butylene oxide and 2.3% water by this method. On the one hand, drying butylene oxide containing as little as 3.5% water by fractionation is impracticable since at least half of the oxide distills as the azeotrope before the water is removed. On the other hand, removal of water by fractionation is said to be practicable when the butylene oxide contains less than about 0.5 weight % water. Under these latter conditions, water is removed as an azeotrope containing 7% water and 93% oxide, leaving the remaining oxide dry. Because the isobutylene oxide/water azeotrope distills at lower temperatures than the water azeotropes of straight chain butylene oxides, the '721 patent further suggests that isobutylene oxide may be advantageously separated from straight chain butylene oxides by azeotropic distillation of the raffinate from the alkaline metal hydroxide extraction step. The patent teaches that the azeotropic column should be a still column having a large number of theoretical plates and that the separation be carried out under a high reflux ratio.
U.S. Pat. No. 3,338,800 teaches extractive distillation of olefin oxides having from 3 to 18 carbon atoms with a paraffin or paraffin naphtha solvent. More particularly, this patent suggests that oxygenated impurities boiling within 5.degree. C. of the olefin oxide may be separated by extractive distillation using as solvents acyclic paraffinic hydrocarbons having boiling points at least 35.degree. C. above the boiling points of the said purities. The problem addressed by this patent is that epoxide fractions produced by the direct oxidation of ethylenically unsaturated compounds with molecular oxygen in the liquid phase contain oxygenated impurities which, because their boiling points are similar to the desired epoxide product, cannot be separated by conventional distillation techniques. The impurities generally include acids, alcohols, aldehydes, ketones and esters. Example 3 of the patent shows extractive distillation of a crude mixture containing 85 weight % isobutylene oxide, 5 weight % ethyl formate and 10 weight % prionaldehyde with an n-octane solvent. The molar ratio of isobutylene oxide:n-octane was 1:11.5 in this example. The overhead temperature was 62.degree. C. and the reboiler temperature was 108.degree. C. Reflux ratio was 40:1. Also see U.S. Pat. No. 3,337,425 which teaches a process similar to the '800 patent except that olefinic naphtha and aromatic hydrocarbons having boiling points at least 35.degree. C. above the impurities are employed as the extractive distillation agent.
U.S. Pat. No. 3,578,568 suggests purifying C.sub.3 -C.sub.5 monoepoxides by extractive distillation with ethylene glycol, propylene glycol, ethylene glycol monomethylether or diethylene glycol monomethylethers.
U.S. Pat. No. 3,838,020 teaches a process for purifying C.sub.3 -C.sub.5 alkylene oxides by extractive distillation using a mixed extractive solvent consisting of at least one solvent selected from the group consisting of 1,3-butylene glycol; 1,4-butylene glycol; isobutylene glycol and glycerine and at least one solvent selected from the group consisting dioxane, butylacetate and 2-ethylhexanol. The method is said to be suitable for purifying crude alkylene oxide streams containing up to about 5 weight % impurities.
An object of the present invention is an improved method for drying butylene oxides, especially straight-chain butylene oxides and particularly 1,2-butylene oxide. A further object of this invention is an improved method for purifying 1,2-butylene oxide produced by epoxidation of 1-butene with an organic hydroperoxide in the presence of the catalyst. Other objects will be apparent from the following description of the invention.